Significant hypotension commonly occurs upon reperfusion of the donor liver. In this study we tried to determine if there is accumulation of prostacyclin in the portal system. Blood samples for prostacyclin in twelve patients undergoing orthotopic liver transplantation were studied. Samples were collected at the beginning and end of portal vein anastomosis. Hemodynamic measurements were determined 1 min before and 3 min after portal revascularization. The results show an increase of prostacyclin from 524 +/- 134 pg/ml (n less than 72 pg/ml) to 1132 +/- 264 pg/ml. Eight patients had a decrease in systolic blood pressure from 98 +/- 5 mmHg to 61 +/- mmHg with concomitant significant increase in cardiac output (6.0) from 6.9 +/- 0.7 to 9.9 +/- 1.05 L/mm and significant decrease in systemic vascular resistance (SVR) from 724 +/- 130 dynes/sec/cm to 309 +/- 98. In conclusion, 60% of patients undergoing OLT accumulate prostacyclin in the portal vein, which could be one of the causes of hypotension seen at reperfusion of the donor liver.